Autolytic yeast extracts are concentrates of the soluble materials obtained from yeast after disruption of the cells and digestion (lysis) of the polymeric yeast material. The active yeast enzymes released in the medium after cell disruption contribute to the lysis. These types of yeast extract are rich in amino acids and generally do not comprise 5′-ribonucleotides because during the autolytic process the native RNA is decomposed or modified in a form which is not degradable into 5′-ribonucleotides. They are used in the food industry as basic taste providers. The amino acids present in the yeast extract add a bouillon-type brothy taste to the food.
Hydrolytic yeast extracts, on the other hand, are concentrates of the soluble materials obtained from yeast after disruption of the cells, digestion (lysis) and addition of proteases and/or peptidases and especially nucleases to the yeast suspension during lysis. The native yeast enzymes are inactivated prior to the lysis. During this process, 5′-ribonucleotides of guanine (5′-guanine mono phosphate; 5′-GMP), uracil (5′-uracil mono phosphate; 5′-UMP), cytosine (5′-cytosine mono phosphate; 5′-CMP) and adenine (5′-adenine mono phosphate; 5′-AMP) are formed. When adenylic deaminase is added to the mixture, 5′-AMP is transformed into 5′-inosine mono phosphate (5′-IMP). The hydrolytic yeast extracts obtained by this method are therefore rich in 5′-ribonucleotides, especially rich in 5′-GMP and 5′-IMP. Often yeast extracts are also rich in mono sodium glutamate (MSG). 5′-IMP, 5′-GMP and MSG are known for their flavour enhancing properties. They are capable of enhancing the savoury and delicious taste in certain types of food. This phenomenon is described as ‘mouthfeel’ or umami.
Yeast extracts rich in 5′-ribonucleotides and, optionally, rich in MSG, are usually added to soups, sauces, marinades and flavour seasonings.
Yeast extracts rich in 5′-ribonucleotides are up to date produced using yeast strains with high RNA content and/or by partial extraction of the cell content.
A disadvantage of this type of taste enhancing hydrolytic yeast extracts is that, due to the presence of amino acids and short peptides and of others yeast components, they are not very suitable for applications which require cleanliness of taste.
U.S. Pat. No. 4,303,680 describes the production of a yeast extract containing 5′-ribonucleotides using an autolytic process under conditions at which the intracellular RNA is only partially decomposed and remains bound to the autolysed cells. The protein content of the cells is hydrolysed in oligopeptides and amino acids. The RNA is enzymatically transformed into 5′-ribonucleotides only after the RNA has been released in solution from the autolysed cells by means of a heat treatment. With this method a yeast extract is obtained which is rich in amino acids, oligopeptides and other components like carbohydrates, minerals, lipids and vitamins. The presence of these components imparts to this yeast extract a bouillon-like, brothy taste which is not desirable in some food applications. A further disadvantage is that the yeast extract comprises a relatively low amount of 5′-ribonucleotides.
An object of the present invention is to provide a process for the production of a composition containing 5′-ribonucleotides which is based on autolysis of a microorganism wherein the composition obtained comprises at least 15% w/w of 5′-ribonucleotides and wherein said composition is clean in taste. The process is very simple and cost-effective and therefore commercially very attractive. Another object of the present invention is to provide compositions containing 5′-ribonucleotides with the above-mentioned characteristics and comprising an amount of 5′-ribonucleotides, based on sodium chloride free dry matter of the composition, of at least 15% w/w and less than 55% w/w. A further object of the present invention is to provide the use of the compositions of the inventions in food, beverages and feed.